Generator Buyers Guide

Generator Buyer's Guide

Generator Guides  »  Generator Buyer's Guide Overview


A generator uses coils of made of copper, which spin inside large magnets at high speeds, in order to convert mechanical energy into electrical energy.

Generator Types

Which type of generator do you need?

Portable Generators

Portable generators can be used in either commercial or residential settings. Commercial portable generators can provide power to a job site for tools such as drills, saws, and air compressors. Residential portable generators can be used to provide emergency power during power outages to the home or business. More info »

PTO Generators

Unlike standard generators, a PTO generator does not contain an engine. PTO generators are used for increased mobility power in farm or ranch environments. They are also cheaper than other generators, as they eliminate the need for a built-in engine.

PTO generators also come with certain accessories, such as trailers that allow the generator to be towed, three point hitch kits, and a drive shaft. More info »

Generator Heads

A generator head is the part of the generator that creates electricity. It will be driven by a separate motor. Generator heads can be purchased individually and connected to an existing engine or motor as a repair part or an upgrade. More info »

Packaged Standby Generators

A standby generator is a backup power system that operates automatically in case of a power outage. Most standby generators run on diesel, natural gas or liquid propane gas. Packaged standby generators come with a housing design that has less exposed bolts and more removable panels for maintenance. More info »

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Before You Buy

Before you select a generator, consider the following:

  • What are your voltage requirements?
  • What are your power requirements? Choose a generator with enough wattage to power the appliances or equipment you need. Don't forget to consider the startup surge power of your equipment.
  • What type of fuel does the generator use?
  • For portable generators, how long can the generator operate until it needs to be refueled?
  • In the case of portable generators, how portable is it? Does it have wheels or handles?
  • What sort of accessories do you need to operate the generator, fuel, drive shaft, power cords, etc?

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Determining Your Wattage Requirements

First you need to determine the wattage of all the items you wish to run on your generator. You can usually find the wattage information on an identification plate or in the manual. If you can't determine the wattage of an item, but you know the AMPs and Volts, you can use the following formula to determine watts.

AMPs x Volts = Watts

To deterime kilowatts (kW) use the following formula.

1,000 Watts = 1 kW

Motor driven equipment is usually listed in horsepower, which needs to be converted to watts. Motors can require up to 4 times as much power to start as they do to run. If the average running wattage for a 1 HP motor is 1000, then the startup surge requirements might be as much as 4,000.

Add the wattage of all tools, appliances, etc. that you are going to run at the same time. Then select a generator with a running wattage that matches or exceeds your total load. Remember to consider the startup wattage requirements of everything you want to run and select a generator with enough wattage to start them, but also keep in mind that you probably won't be starting everything at the same time.

Consult the following chart to determine an estimate for your total load requirements:

Household / RV Average Running Wattage Surge Wattage Required for Startup
Central Air Conditioner, 10,000 BTU 1500 2200
Clothes Washing Machine 1150 2300
Coffee Maker 1750 0
Dishwasher (Cool Dry) 700 1400
Electric Clothes Dryer 5750 1800
Electric Frying Pan 1300 0
Electric Range, 8 Element 2100 0
Furnace Fan, Gas or Oil, 1/8 HP 300 500
Furnace Fan, Gas or Oil, 1/6 HP 500 750
Furnace Fan, Gas or Oil, 1/4 HP 600 1000
Furnace Fan, Gas or Oil, 1/3 HP 700 1400
Furnace Fan, Gas or Oil, 1/2 HP 875 2350
Hair Dryer 300-1200 0
Iron 1200 0
Lights As Indicated on Bulb 0
Microwave, 625 Watts 625 800
Radio 50 - 200 0
Refrigerator or Freezer 700 2200
RV Air Conditioner, 7,000 BTU 1700 600
RV Air Conditioner, 10,000 BTU 2000 700
RV Air Conditioner, 15,000 BTU 3500 1500
RV Air Conditioner, 13,500 BTU 2750 1250
Sump Pump, 1/3 HP 800 1300
Sump Pump, 1/2 HP 1050 2150
Television 300 0
Toaster 1050-1650 0
Well Pump, 1/2 HP 1000 2100
Vacuum Cleaner 800-1100 0
Contractor Average Running Wattage Surge Wattage Required for Startup
Air Compressor, 1/2 HP 975 1600
Air Compressor, 1 HP 1600 4500
Bench Grinder, 8" 1400 2500
Circular Saw, 7-1/4" 1400 2300
Drill, 4 AMP, 3/8" 440 600
Drill, 5.4 AMP, 1/2" 600 900
Electric Chain Saw, 2 HP, 14" 1100 0
Electric Welder, 200 AMP AC 9000 0
Electric Welder, 230 AMP AC, at 100 AMP 7800 0
Hand Drill, 1/2" 600
High Pressure Washer, 1 HP 1200 3600
Table Saw, 10" 1800 4500
Industrial Motors Average Running Wattage Surge Wattage Required for Startup
Split Phase, 1/4 HP 600 1000
Split Phase, 1/2 HP 875 2300
Capacitor Start, Induction Run, 1/3 HP 720 1300
Capacitor Start, Induction Run, 1 HP 1600 4500
Capacitor Start, Capacitor Run, 1-1/2 HP 2000 6100
Fan, 1/6 HP 550 850
Farm Equipment Average Running Wattage Surge Wattage Required for Startup
Battery Charger, 15 AMP 380 0
Battery Charger, 60 AMP with 250 AMP Boost 1500 / 5750 0
Battery Charger, 100 AMP with 300 AMP Boost 2400 / 7800 0
Electric Fence, 25 Miles 250 0
Grain Cleaner, 1/4 HP 650 1000
Milk Cooler 1100 1800
Milker (Vacuum Pump), 2 HP 1000 2300
Portable Heater, Kerosene or Diesel, 50,000 BTU 400 600
Portable Heater, Kerosene or Diesel, 90,000 BTU 500 725
Portable Heater, Kerosene or Diesel, 150,000 BTU 625 1000
Computers Average Running Wattage Surge Wattage Required for Startup
Desktop 600 - 800 0
Fax Machine 600 - 800 0
Laptop 200 - 250 0
Monitor 200 - 250 0
Printer 400 - 600 0

*All ratings are estimates. Contact the manufacturer of your item for exact requirements.

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Fuel Types


Gasoline has some significant advantages over other fuel sources: it is generally the cheapest, most common, and most easily attainable. The cost of a gasoline engine is also very inexpensive, but the life of the engine can be short, depending on the type of engine being used.

Gas also has a short shelf life and is highly flammable, making it hazardous to store. It can contain poisonous vapors and may form gum deposits during cold starting.

Liquid Propane (LP)

Propane, as opposed to gasoline, is easily stored and has a long shelf life. It is also is clean burning and can be obtained during power outages, while gasoline may not. It will also have no issues during cold starting.

The downsides of liquid propane include the cost, which can be high depending on local prices. Propane powered generators might cost as much as 20% higher for those that are 30 kW or higher.

When compared to diesel engines, propane requires up to three times as much fuel and the engines have a shorter lifespan.

Natural Gas

Natural Gas is clean burning, quieter, and is an unlimited source that does not require refueling. It also experiences no problems during cold starting/operation.

While natural gas will be available during power outages, it may not be during natural disasters, such as earthquakes. It also is not available in many areas and, like propane, might require up to three times as much fuel by volume than diesel.


Diesel is the least flammable, and therefore is the safest, fuel source. Diesel fuel is easy to find, especially during disasters since it is used by the military, as well as the trucking and farming industries. Diesel also does not ferment when it is in the tank for long periods of time, as gasoline does, and will not form gum deposits during cold operation. Diesel engines have excellent life expectancy, some lasting up to 20,000 hours of operation.

Unfortunately, diesel has a short shelf life, only lasting two years at the most. Even though it is the easiest fuel to obtain during a natural disaster, it might not be available during power outages. Diesel engines are also noisier than other engines.

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Power Capacity

To determine the wattage of the items you wish to run on your generator, you can usually find the information on an identification plate or in the application manual.

If you cannot find this information, you determine the wattage simply by multiplying the AMPs and volts. For three phase loads, the wattage is determined by multiplying Amps by Volts by 1.732 (square root of three). 1,000 watts will be equal to 1 kilowatt.

Add up the wattages of all applications that will be hooked up to the generator, then select a generator with a running wattage that matches or exceeds the total running wattage put together. You may also want to select a generator with a starting wattage that is the same or higher than the total, but remember that you probably won't be starting everything at the same time. If you are planning on running large motor loads on the generator, make sure that the generator has a motor starting ability that is sufficient for the HP rating of your largest motor load.

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Generator Safety

Generators should not be used indoors, as ample ventilation is needed during operation. This includes garages, basements, crawlspaces, and sheds.

Generators should be used far from doors, windows, and vents that might allow carbon dioxide emissions to come inside. If you begin to feel dizzy or weak while operating your generator, get to fresh air right away.

Do not attempt to backfeed your generator by connecting it directly to the circuits or wiring of your home. Instead, plug your generator into a transfer switch installed by an electrician. This will prevent the generator from sending power back into the utility lines. Backfeeding is extremely dangerous and presents an electrocution risk to utility workers and neighbors served by the same utility transformer. It also bypasses some of the built-in household circuit protection devices. Using a transfer switch instead will protect your generator and home wiring from damage when power is restored.

Before refueling your generator, turn it off and allow it to cool down. Avoid spilling fuel on hot components as it could ignite, and put out all flames or cigarettes when handling the fuel. Always have a fully charged, approved fire extinguisher near your generator.

Don't overload the generator. Use only when necessary to power essential equipment. Use heavy-duty extension cords from the generator, as overloaded cords can cause fires and equipment damage. Make sure cords are placed to avoid tripping hazards, but don't put underneath carpets where heat may build up.

If you must use your generator in wet conditions, protect it from moisture to prevent electrocution hazard to yourself and damage to the generator. Do not operate your generator indoors, but under an open canopy-like structure on a dry surface where water can not reach it or pool underneath it. Be cautious handling electrical cords in wet conditions. Ensure your hands are dry when using your generator and handling cords.

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